Endocrine complications after radiotherapy for tumors of the head and neck are thought to be relatively rare. In radiotherapy of nasopharyngeal cancer, the paranasal sinuses, optic nerves neoplasms and intracranial tumors other than the pituitary, the hypothalamic pituitary axis, and the thyroid gland in presence of lymph gland metastasis to the neck are invariably included in the field of high dose irradiation. Our preliminary investigations have shown that hypopituitarism secondary to hypothalamic lesion or primary pituitary damage may be more common than suspected in the past and that primary hypothyroidism may result from irradiation of the regional neck nodes. Prospective study of this group of patients is warranted to determine the latent period between radiotherapy and development of endocrine complications and initiate treatment early. The dose, technique, and period of raditherapy will be determined in correlation with the endocrine results. This information may enable us to minimize the endocrine complication without compromising treatment. Children with leukemia now have an improved life span. Some of these children receive chemotherapy alone while others receive chemotherapy and prophylactic irradiation of the brain. Endocrine evaluation of these two groups of patients who are now living five years or longer is needed to determine the effect of prophylactic radiotherapy. Patients with Hodgkin's disease and chronic lymphocytic leukemia involving the neck lymph glands often receive radiotherapy to the neck area. Determination of the thyroid and parathyroid function in this group of patients compared to a similar group who received no neck irradation should be seriously evaluated in correlation with the dose of irradiation.